Overview
What you’ll learn
- Model the three states of matter and name every change of state in both directions.
- Explain ionic bonding and deduce ionic formulae from ion charges.
- Draw dot-and-cross diagrams for ionic compounds and covalent molecules.
- Explain melting-point and conductivity differences between ionic compounds, simple molecules and giant structures.
- Describe polymers, metals and alloys, linking structure to properties.
- Match each carbon allotrope to its structure, properties and uses.
Specification checklist (AQA Trilogy 8464 · Edexcel 1SC0 · OCR Gateway J250)
Statements are paraphrased from the shared DfE combined science subject content and grouped by tier. Foundation content is studied by every student; Higher statements are examined on Higher-tier papers only. This chapter covers only what Combined Science (double award) examines — separate-science extras live on the GCSE Biology, Chemistry and Physics hubs. QuizQuip is not affiliated with AQA, Pearson Edexcel or OCR.
Foundation — every student
- 12.1Describe the three states of matter in the particle model, the changes of state between them, and conservation of mass during changes of state.
- 12.2Describe ionic bonding: metal atoms losing electrons and non-metal atoms gaining them to form ions with full outer shells, held together by strong electrostatic forces in a giant lattice.
- 12.3Deduce the formulae of ionic compounds from the charges of their ions and draw dot-and-cross diagrams for simple ionic compounds.
- 12.4Describe covalent bonding as the sharing of electron pairs in simple molecules and giant structures, and draw dot-and-cross diagrams for molecules such as H₂, HCl, H₂O, CH₄, O₂ and NH₃.
- 12.5Explain the properties of ionic compounds (high melting points, conduction when molten or dissolved) and of simple molecular substances (low melting points, no conduction) in terms of their bonding and structure.
- 12.6Describe polymers as long covalently bonded chains and metals as giant lattices of positive ions in a sea of delocalised electrons, and explain their properties, including why alloys are harder than pure metals.
- 12.7Describe the allotropes of carbon — diamond, graphite, graphene and fullerenes — linking each structure to its properties and uses.
Key points
- 1States: solid (fixed, vibrating), liquid (moving, touching), gas (fast, far apart). Melting ⇄ freezing; boiling ⇄ condensing; sublimation skips the liquid.
- 2Changes of state are physical — mass is conserved and the substance itself is unchanged.
- 3Ionic bonding: metal loses electrons, non-metal gains them; oppositely charged ions attract in a giant lattice.
- 4Ionic formulae: balance the charges — Al³⁺ needs 3 × Cl⁻ to give AlCl₃; work with common ions (SO₄²⁻, NO₃⁻, CO₃²⁻, OH⁻).
- 5Covalent bonding: atoms share electron pairs to complete outer shells — H₂, H₂O, CH₄, NH₃, O₂ (double bond).
- 6Ionic compounds: high melting points (strong forces in the lattice), conduct only when molten or dissolved (ions free to move).
- 7Simple molecules: weak intermolecular forces → low melting/boiling points; no charged particles → never conduct.
- 8Polymers: giant covalent chains, strong covalent bonds within, weak forces between — usually solid at room temperature.
- 9Metals: positive ions in a sea of delocalised electrons → conduction of heat and electricity, and layers that slide (malleable). Alloys mix atom sizes so layers jam — harder than pure metals.
- 10Carbon allotropes: diamond (4 bonds, hardest, no conduction), graphite (3 bonds, layers slide, conducts), graphene (one layer, strongest), fullerenes (cages/tubes, drug delivery).
Notes · 1 of 6
States of matter and changes of state
Three arrangements of the same particles — and the energy that flips them.
| State | Particle arrangement | Movement | Shape |
|---|---|---|---|
| Solid | Regular, touching | Vibrate about fixed positions | Fixed shape, fixed volume |
| Liquid | Random, touching | Move around each other | Takes container’s shape, fixed volume |
| Gas | Random, far apart | Fast, straight lines until collisions | Fills any container |
Melting, freezing, boiling, condensing and sublimating are all physical changes: the particles themselves never change, only their arrangement and energy. Mass is conserved — 50 g of ice melts into exactly 50 g of water. Boiling needs a bigger energy jump than melting because separating particles completely takes far more energy than loosening them.
Notes · 2 of 6
Ionic bonding
Electron transfer, full shells, and an unstoppable electrostatic grip.
Metals sit low in electronegativity and hand over their outer electrons; non-metals accept them. Both finish with full outer shells. The metal becomes a positive ion, the non-metal a negative ion, and the opposite charges attract — an electrostatic force strong enough to build a giant lattice of alternating ions.
Worked example — deducing an ionic formula
Aluminium oxide: aluminium forms Al³⁺, oxygen forms O²⁻. Charges must cancel: 2 × (+3) = +6 and 3 × (−2) = −6, so the formula is Al₂O₃. Swap-and-check: the charge number of one ion becomes the count of the other. With polyatomic ions the brackets matter — calcium hydroxide is Ca(OH)₂, not CaOH₂.
Dot-and-cross diagrams tell this story visually: dots for the metal’s electrons crossing to circles (crosses) for the non-metal. Sodium chloride shows one electron moving from Na to Cl, leaving Na⁺ and Cl⁻ with full shells. For the exam you only need single ion pairs in square brackets with their charges.
Notes · 3 of 6
Covalent bonding
Sharing is caring — pairs of electrons gluing non-metals together.
| Molecule | Bonds | Shared pairs |
|---|---|---|
| H₂ | H–H | 1 |
| HCl | H–Cl | 1 |
| H₂O | O with two H | 2 |
| CH₄ | C with four H | 4 |
| O₂ | O=O | 2 (a double bond) |
| NH₃ | N with three H | 3 |
In dot-and-cross diagrams, each shared pair is one covalent bond. Every atom should finish with a full outer shell — hydrogen counts a full shell as 2. Carbon shares four times (methane), nitrogen three times with a lone pair left over (ammonia).
Notes · 4 of 6
Structure explains properties
Melting points and conductivity, decoded from bonding.
| Structure | Melting point | Conducts? | Why |
|---|---|---|---|
| Ionic (giant lattice) | High | Only when molten or dissolved | Strong electrostatic forces; ions free to move only when the lattice breaks up |
| Simple molecular | Low | Never | Weak intermolecular forces between molecules; no charged particles anywhere |
| Giant covalent | Very high | Usually no (graphite/graphene yes) | Strong covalent bonds throughout must be broken to melt |
| Metallic | Usually high | Yes | Delocalised electrons carry charge through the lattice |
The intermolecular point trips people up: when ice melts, no covalent bonds break — only the weak forces between molecules are overcome. In giant structures there are no separate molecules, so the strong bonds themselves must break, demanding far more energy.
Notes · 5 of 6
Polymers, metals and alloys
Long chains, electron seas, and jammed layers.
Polymers are enormous covalent molecules — thousands of repeated units in one chain. The covalent bonds inside each chain are strong; the forces between chains decide whether the polymer is flexible (weak forces, e.g. polythene bags) or rigid and strong (stronger forces or cross-links).
Metals are a giant lattice of positive ions surrounded by delocalised electrons — the outer electrons detach and belong to the whole metal. This explains everything: the electrons carry charge (conduction) and heat energy; the ions are held in layers that can slide over each other, making metals malleable. Add a different-sized atom — an alloy — and the layers distort and jam: alloys are harder than pure metals, which is why bronze outlasted pure copper tools.
Notes · 6 of 6
The allotropes of carbon
One element, four structures, four personalities.
| Allotrope | Structure | Key properties | Uses |
|---|---|---|---|
| Diamond | Each C bonded to 4 C in a rigid giant lattice | Hardest natural material; very high melting point; does not conduct | Cutting tools, jewellery |
| Graphite | Each C bonded to 3 C in layers; one delocalised electron per atom | Layers slide (lubricant, pencils); conducts electricity | Pencil “lead”, electrodes, lubricant |
| Graphene | A single graphite layer, one atom thick | Extremely strong and light; conducts | Electronics, composites |
| Fullerenes | Caged molecules (C₆₀ buckyballs) or nanotubes | Large surface area; hollow; strong for their size | Drug delivery, lubricants, reinforcing materials |
The graphite–diamond contrast is the classic exam question. Same element, different bonding counts: four bonds lock diamond rigid with no free electrons; three bonds leave each carbon’s fourth electron delocalised between layers — free to conduct, while the weak layer forces let the sheets slide off onto paper as pencil marks.
Revise
Key terms
The words examiners expect you to use precisely.
- Change of state
- A physical change between solid, liquid and gas; mass is conserved.
- Ion
- An atom that has lost or gained electrons, giving it a charge.
- Ionic bond
- The strong electrostatic attraction between oppositely charged ions.
- Giant lattice
- A huge, regular, repeating structure of particles.
- Covalent bond
- A shared pair of electrons between two atoms.
- Intermolecular force
- The weak attraction between separate molecules, overcome when they melt or boil.
Show 6 more key termsShow fewer key terms
- Polymer
- A giant molecule of thousands of repeated covalently bonded units.
- Delocalised electron
- An electron not tied to one atom, free to move through the structure.
- Alloy
- A mixture of a metal with other elements, distorting the lattice to make it harder.
- Allotrope
- Different structural forms of the same element, such as diamond and graphite.
- Graphene
- A single layer of graphite — one atom thick, very strong and conductive.
- Fullerene
- A cage-like carbon molecule (e.g. C₆₀) or nanotube with a hollow interior.
Revise
Common mistakes
Where students most often lose marks in this chapter — and what to do instead.
Mistake: Saying covalent bonds break when simple molecules melt
Only weak intermolecular forces are overcome.
Instead: Melting separates molecules; the covalent bonds inside stay intact.
Mistake: Writing NaCl₂ or CaOH₂
Charges must cancel in ionic formulae.
Instead: Na⁺ + Cl⁻ → NaCl; Ca²⁺ + 2 OH⁻ → Ca(OH)₂ — brackets for multiples of polyatomic ions.
Show 10 more mistakesShow fewer mistakes
Mistake: Claiming ionic solids conduct electricity
Ions are locked in the lattice when solid.
Instead: Ionic compounds conduct only when molten or dissolved, when ions are free to move.
Mistake: Saying simple molecular substances conduct when dissolved
Dissolving a sugar or ethanol molecule makes no ions.
Instead: No charged particles, no conduction — unlike ionic solutions.
Mistake: Drawing methane with two shared pairs
Carbon makes four single bonds in methane.
Instead: CH₄ = four shared pairs; O₂ = the double-bond case.
Mistake: Explaining metal conduction with moving ions
The ions stay fixed in the lattice.
Instead: Delocalised electrons drift and carry the charge.
Mistake: Forgetting why alloys are harder
Same-size layers slide just as easily.
Instead: Different-sized atoms distort the layers so they cannot slide.
Mistake: Saying graphite conducts because of free ions
There are no ions in graphite.
Instead: One delocalised electron per carbon carries charge along the layers.
Mistake: Claiming diamond conducts electricity
All four outer electrons are used in bonds.
Instead: No delocalised electrons, so diamond cannot conduct (but it does conduct heat well).
Mistake: Mixing up mass changes at state changes
Particles are neither created nor destroyed.
Instead: Changes of state are physical; mass is conserved throughout.
Mistake: Calling graphene “a big diamond”
Graphene is one layer of graphite, not diamond.
Instead: Graphene = single hexagonal graphite layer; diamond = rigid 3D four-bond lattice.
Mistake: Using “weak bonds” for intermolecular forces
Examiners want “forces”, not “bonds”.
Instead: Intermolecular FORCES between molecules are weak; covalent BONDS inside are strong.
Check yourself
Quick quiz
20 questions with instant explanations. About 5 minutes.
Question 1 of 3· free preview of 20
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Explain ionic bonding
An ionic bond is the electrostatic attraction between
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Practise
Topical questions
12 exam-style questions with model answers and mark schemes.
A set of structured and calculation questions matched to this chapter, in three tiers, each with a model answer, mark scheme and examiner tip. Higher-tier questions are tagged.
Practise topical questionsExam practice
Practice paper
A 30-mark paper in the style of a Combined Science paper, with a separate mark scheme. Give yourself 40 min.
Question paper
Chapter 12 Practice Paper
30 marks · 40 min · 5 pages
6 multiple-choice questions and structured questions with answer lines. States of matter, ionic, covalent and metallic bonding, ionic formulae and dot-and-cross diagrams, structure–property links, polymers and alloys, and the allotropes of carbon.
Mark scheme
PROChapter 12 Practice Paper — mark scheme
Answers · Marking points · 3 pages
Model answers with a mark for each creditworthy point — for marking at home or in class.
How does this chapter fit the real exams?
Chemistry Paper 1
1 h 15 · 70 marks (Trilogy)
Atomic structure, bonding, quantitative chemistry, chemical and energy changes (chapters 11–16)
Chemistry Paper 2
1 h 15 · 70 marks (Trilogy)
Rates, organic chemistry, analysis, atmosphere and resources (chapters 17–20)
Tiers
Foundation (grades 1-1 to 5-5) · Higher (4-3 to 9-9)
Two grades are awarded together; the 21 required practicals are examined on the written papers
Want a full paper? Try the Biology Paper 1-style (Foundation), Biology Paper 1-style (Higher), Biology Paper 2-style (Foundation), Biology Paper 2-style (Higher), Chemistry Paper 1-style (Foundation), Chemistry Paper 1-style (Higher), Chemistry Paper 2-style (Foundation), Chemistry Paper 2-style (Higher), Physics Paper 1-style (Foundation), Physics Paper 1-style (Higher), Physics Paper 2-style (Foundation), Physics Paper 2-style (Higher), Required practicals practice sets.
Questions
Frequently asked questions
How is Combined Science bonding different from triple Chemistry?
The core is identical — states, ionic/covalent/metallic bonding, structure–property links and carbon allotropes. Triple adds nanoparticles and more quantitative work, which are not examined in Combined Science.
Which maths skills appear in this chapter?
Deducing formulae by balancing ion charges — ratio reasoning rather than calculation.
How do I quickly write an ionic formula?
Write the ions with charges, swap the charge numbers as subscripts, and use brackets for polyatomic ions. Check the charges cancel.
Why do “weak forces” matter more than “weak bonds”?
Examiners award the word “forces”. Intermolecular forces between molecules are weak; the covalent bonds inside molecules are strong and never break during melting or boiling.
What is the single best bonding fact for conductivity?
Only mobile charged particles conduct: delocalised electrons in metals and graphite, free ions in molten or dissolved ionic compounds — and nothing else.
Up next
Chapter 13: Quantitative chemistry